There are more than two endings. I think, if I remember correctly, the total number is 4 or 5. The longer ending, according to one manuscript, was written by Aristion the Elder, who apparently was the same person known to Papias of Hierapolis (who wrote c. 130) as a major source of oral traditions about Jesus and the apostles. There is also the Freer Logion, which appears in one MS and which was reported by one of the church fathers.
The gospel otherwise ends at v. 8 in mid-sentence, and at a crucial narrative moment -- leaving certain expectations in the narrative unfulfilled. A resurrection appearance in Galilee is hinted in v. 7 and earlier in 14:28, but no such apperance is related -- indeed, the risen Jesus is never seen at all in this gospel. Instead it ends on an odd note of the women being seized by fear and unable to relate their discovery of the empty tomb. However, such an appearance in Galilee is related in the appendix to the gospel of John, in ch. 21. If the ending of Mark was mutilated, then it possibly ended with a story like this. But what is striking about this story is that it is closely parallel to the miracle story in Luke 5:1-11. And that story concerned the initial call of Peter, Andrew, and the sons of Zebedee. In the gospel of Mark, the parallel to this story is in the very first chapter, 1:16-20. So the mutilation of the gospel, if this is what took place, had a very interesting effect. The reader expects to find a resurrection appearance of Jesus in Galilee. But this story is missing. In order to find Jesus appearing in Galilee, the reader has to go back to the very beginning of the story where Jesus is baptized and then appears in Galilee to Peter, Andrew, and the sons of Zebedee (ch. 1). In other words, there is a circularity in the narrative that seems to have a theological basis. The circularity hinges on the equivalence of baptism with death/resurrection. This is explicitly stated as such in ch. 10. Jesus asks the sons of Zebedee if they could drink the cup he must drink "or be baptized with the baptism with which I must be baptized" (10:39). So just prior to his death, Jesus speaks about receiving a "baptism" through martyrdom. This again encourages the reader to connect Jesus death and resurrection with the baptism related in ch. 1, which immediately is followed by Jesus' initial meetings of his disciples in Galilee. This connection between baptism and death is also part of Pauline theology:
"You have been taught that when we were baptized in Christ Jesus we were baptized in his death; in other words, when we were baptized we went in the tomb with him and joined him in death, so that as Christ was raised from the dead by the Father's glory, we too might live a new life. If in union with Christ we have imitated his death, we shall also imitate him in his resurrection" (Romans 6:2-5).
BTW, there are a few other signs of mutilation and/or redaction in the book. This is especially clear if you compare the present text of Mark with the text reproduced by Matthew and Luke, who seem to have used an earlier verison of it. Check out also 1:1-4, 10:46, 14:51-52, and a few other places where there seem to be signs of redaction, or where there are unusual narrative features.
